This investigation is designed to evaluate the role of RNA Polymerase enzyme in gene expression in a eukaryotic system capable of differentiation. The system selected for this study is a slime mold, Physarum polycephalum. The slime molds usually require an association with living or dead bacterial cells for growth and reproduction. Only in rare instances does a slime mold grow and reproduce in pure culture. Recent advances in the culturing techniques of P. polycephalum enable this organism to be propagated in a culture medium in the absence of living or dead bacterial cells. Therefore, this organism was selected because of recent biochemical studies on it which have laid the foundation for this investigation. The primary objectives of this study are: (1) to isolate RNA Polymerase core enzyme and sigma factor(s) in the microplasmodial stage of growth and to biochemically characterize the polymerase products by DNA-RNA hybridization studies; (2) to isolate RNA polymerase core enzyme and sigma factor(s) in the sporulation stage of development and to biochemically characterize the polymerase products by DNA-RNA hybridization studies; (3) to isolate nuclear DNA from microplasmodial stage of growth to be used as template for assay and for hybridization studies; and (4) to perform cross-competition hybridization studies of the actual products produced from transcription to evaluate differential gene activity during different stages of growth (differentiation).